A photographic process using light-sensitive silver halide is widely used because it is superior to other photographic processes such as an electrophotographic process or a diazo photographic process in photographic characteristics such as sensitivity and gradation control. Recently a method of processing a silver halide light-sensitive material has been developed which makes it possible to form images in a simplified manner and quickly employing dry processing, in which the light-sensitive material is developed by heating, in place of the conventional wet processing process in which the light-sensitive material is developed using a conventional wet developer.
A heat-developable light-sensitive material is known in the art; the heat-developable light-sensitive material and a process of processing the light-sensitive material are described in, for example, Shashin Kogaku no Kiso (Fundamentals of Photographic Engineering), pp. 553-555 (Corona Co., Ltd., Tokyo, (1979)), Eizo Gaho (Image Information), page 40, (April 1978), Nebletts Handbook of Photography and Reprography, pp. 32-33, Van Nortrsnd Reinhold Co., 7th Ed (1977), U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, 3,457,075, British Patent Nos. 1,131,108, 1,167,777, and Research Disclosure, June 1978 (RD-17029), pp. 9-15.
Many methods are known for forming color images. One method is to form a color image by reacting an oxidation product of a developer and a coupler. Using this method, U.S. Pat. No. 3,531,286 describes p-phenylenediamine-based reducing agents and phenolic or active methylene couplers. In addition, U.S. Pat. No. 3,761,270 describes p-aminophenol-based reducing agents; Belgian Patent No. 802,519 and Research Disclosure, Sept. 31, 1975, page 32, disclose sulfonamidophenol-based reducing agents; and U.S. Pat. No. 4,021,240 disclose a combination of a sulfonamidophenol-based reducing agent and a fourequivalent coupler.
Another method forms positive color images by the light-sensitive silver/dye bleaching process. Useful dyes and bleaching methods are described in, for example, Research Disclosure, April 1976 (RD-14433), pp. 30-32, Research Disclosure, December 1976 (RD-15227), pp. 14-15, and U.S. Pat. No. 4,235,957.
Further, another method is to form a color image by heat development, utilizing compounds having a dye portion and capable of releasing a mobile dye in a positive or negative relation to the reduction of silver halide into silver. This method is described in U.S. Pat. Nos. 4,500,626, 4,483,114, Japanese Patent Application (OPI) Nos. 28928/83 (corresponding to U.S. patent application Ser. No. 582,655 filed on Feb. 23, 1984), and U.S. Pat. No. 4,503,137 (the term "OPI" as used herein means a "published unexamined Japanese patent application").
In these image-forming methods, organic silver salts are usually incorporated in the light-sensitive material for the purpose of accelerating heat-development. Addition of such organic silver salts, however, results in a serious disadvantage, i.e. the sensitivity of the light-sensitive material in which a silver halide emulsion sensitized with a sensitizing dye and the organic silver salt are present in combination is decreased during its storage.